1. Technical Field of the Invention
The present invention relates to the field of torque transmitting members, such as power shafts, having inherent or intrinsic parameter measurability. The present invention also relates to a method of fabricating such torque transmitting power shaft members having inherent parameter measurability. In particular, the parameters that are measurable by virtue of the inherent structural nature of the power shaft of the invention include the torque applied to the shaft which is directly related to the twist of the shaft, the speed of shaft rotation, as well as both the frequency and amplitude of the torsional oscillations excited by pulsating source and shaft load characteristics. Moreover, having measured the torque and speed of the shaft, the horsepower can readily be obtained.
2. Description of Background of Invention
In virtually every industrial application conceivable, and particularly in the field of aircraft propulsion, rotating shafts are used to transmit and apply torque. It is frequently desirable, in the broad range of such applications, to be able to perform an accurate and efficient measurement of the torque applied to a rotating shaft. Such a torque measurement can be used to control or monitor the operation of the system within which the rotating shaft is utilized.
Similarly, it is often desirable to be able to provide an accurate and efficient measurement of the speed at which a shaft is rotating. Such speed measurement can also be used to control and monitor the operation of the various components of the system within which the rotating shaft is employed.
Further, it is frequently both necessary and desirable to be capable of measuring the horsepower transmitted by a driven shaft. Further, in many situations, a measurement of not only the average transmitted torque, but also the frequency and amplitude, of the torsional oscillation components that comprise the average torque, are also necessary.
The purpose of such control and monitoring can be quite varied. Such measurements can be used to avoid or warn of the approach of the monitored or controlled member to its design limits. Thus, catastrophic failure of the member under excessive torque or at high speeds can be avoided. Overstressing of the member, which can occur by applying excessive torque thereto, can also jeopardize the useful lifetime of the member by accelerating the fatigue failure of the member. For all of the above reasons and many others, it has long been known that accurate and efficient torque and speed measurements are desirable in a wide variety of applications.
In the prior art, numerous examples of torque and speed measuring devices are known and have been applied to rotating shafts of all sorts and within all types of environments. These prior art torque and speed measuring devices utilize various known physical principles for measuring the speed and torque of the shaft member.
Torque and speed measuring devices that utilize either variable reluctance sensors or optical Faraday rotators are known. To use such known sensors, a rotating shaft generally includes two toothed members which define discrete sensible discontinuities about the rotating shaft. These two members are positioned adjacent to each other and are mounted and affixed to the shaft at locations spaced a predetermined distance apart from each other. Thus, shaft rotation and shaft twisting under the application of a torque load results in the generation of a pulse string by the sequential movement of the sensible discontinuities past an appropriately positioned and appropriately configured sensor.
In a preferred embodiment, toothed members that define the discrete, sensible discontinuities comprise first and second gears or gear-like members. The gears are each provided with the same number of teeth and are configured such that the teeth of one gear are positioned between the teeth of the other gear. The sensing element, which, in the preferred embodiment comprises a single pole sensor, is positioned externally of the torque transmitting shaft at the interface between the adjacent gears, and in direct proximity to the intermeshed gear teeth. The sensor is arranged to detect the spacing between teeth as the spacing varies with applied torque.
The sensor, which can either be a variable reluctance, an optical/Faraday rotator, or can utilize any other sensing technology capable of magnetically discerning the relative positions of the intermeshed teeth as they pass by the sensor during shaft rotation, detects the magnetic center of each tooth as it passes the sensor location and consequently produces an output pulse train in which the phase relationship of adjacent pulses represents the relative rotational positions of the adjacently positioned gear-like members located within the composite shaft. The relative rotational positions of the gear-like members are dictated by the amount of torsional deflection in the composite power shaft, and thus provide a signal directly related to the transmitted shaft torque. The gear-produced signal can also be utilized to sense the operating temperature of the rotating shaft. This can be utilized to compensate for variation in the shaft twist due to temperature and results in the very accurate torque measurements required in many applications.
With respect to speed, the same gear-like elements carrying the discrete discontinuities can be sensed in any similar, conventional manner to yield a resultant signal which will be an accurate measure of the rotary speed of the shaft. As the sensing device in either of the above two environments, a single pole magnetic sensor, or a single pole fiber optic sensor is conventionally utilized.
In certain modern day applications, metal torque transmitting members are being replaced more and more by high strength shafts formed of composite materials. This move towards the use of non-metallic composite materials is particularly prevalent in the aircraft industry where both high strength and low weight are prime considerations. Many of these composite materials comprise fiber reinforced resin matrix compositions. The composites from which these drive members can be fabricated include, but are not limited to, boron and/or carbon fibers embedded in a solid resin matrix.
In accordance with the aims and needs outlined above, often, torque transmitting shafts and other members in these various diverse environments are provided with sensing portions attached thereto to be sensed by adjacently positioned sensors to yield a measurement of the torque to which the shaft is subjected. One serious problem with such prior art torque measuring mechanisms is that the shaft must be provided with a through hole or other aperture to enable the sensor positioned externally of the shaft to sense the rotation of sensing portions attached to the shaft. This rotation is related to the twist of the shaft and, thus, to the torque applied to the shaft and is the sensed parameter in many of the prior art torque and speed sensing and measuring devices.
However, providing an aperture in the torque transmitting shaft poses several significant problems. Firstly, it provides a severe weakening in the load bearing and torque transmitting capability of the shaft, thus decreasing the usefulness of the shaft, particularly in the high torque applications which very often are required in many environments. Secondly, such through holes often produce unpredictable stress concentrations which are very undesirable in these environments. Because of the extremes of temperature at which many torque transmitting shafts and other members are often utilized, such unpredictable stress concentrations and non-uniformity in the thermal reactions (i.e., expansion) must be avoided. Further, the provision of through holes allows dust and other contaminants to enter the shaft. Through holes or arrangements where the gear teeth are mounted exteriorly of the shaft also allow the teeth to become chipped or otherwise damaged. A chipped tooth can result in a distorted signal output and is thus to be avoided. Further, by having the reference sleeve entirely within the shaft, the entire shaft exterior surface remains visible. This facilitates visual inspection of the shaft surface, such as for fatigue cracks and similar defects.
Moreover, as discussed above, the use of composite materials to fabricate a torque transmitting shaft, would also provide a very significant reduction in shaft weight. Besides being desirable in and of itself, such weight reduction in many applications is operative to raise the critical speed of the shaft above the level of design concern.
Thus, there has been a very long felt, and significant need in the field for torque transmitting members having the capability of providing a sensing element to be sensed by an appropriate torque measurement sensor device which is free from the above-discussed deficiencies. In particular, it would be advantageous if such a sensing mechanism could be provided that did not require deforming or providing apertures or holes in the structure of the shaft itself. It is this need in the art that the present invention is designed to solve and, in fact, does solve in a very efficient and cost effective manner.
It is therefore among the objects of the present application to provide a torque transmitting member, such as a shaft, not suffering from the above-described deficiencies. In particular, it is an object of the present application to provide a torque transmitting shaft that provides a sensing element, sensible from outside the shaft, without requiring the provision of apertures in the wall of the shaft. It is a further object of the present invention to provide a method of forming such a shaft and for sensing the relative movement between interiorly disposed reference members secured to such a shaft, whose relative locations vary in accord with the transmitted shaft torque. Such a shaft, in addition to being capable of generating signals related to the torque transmitted by the shaft, can also be utilized to indicate the speed of the shaft, its transmitted horsepower, as well as the frequency and amplitude of torsional oscillations caused by pulsating load and source characteristics.